In fields, such as organic electronics and food packaging, a need is recently being felt for a material having lower water vapor permeability and/or oxygen permeability than up to now, more specifically a material, such as a film or sealing material having higher gas barrier properties than in the past. A high-sensitivity technology for evaluating gas barrier properties is therefore needed for the development of new materials and the inspection of products prior to shipment.
Methods for evaluating the gas barrier properties of a sample in the form of film are generally classified into an equal-pressure method and a differential-pressure method. The equal-pressure method refers to a method according to which a gas containing a test gas is introduced onto one surface (hereinafter, referred to as feed side) of the sample, and a carrier gas, such as nitrogen, is introduced onto the other surface (hereinafter, referred to as permeation side), and concentration of the test gas that permeated through the sample and is contained in the discharged carrier gas is measured by a detection unit comprising an infrared sensor or the like (Non-Patent Literature 1, Non-Patent Literature 2). A method is known in which a quartz resonator moisture meter or a mass spectrometer is used for high-sensitivity evaluation, and a system is also known in which the space on the permeation side is temporarily closed to concentrate the test gas permeated through the sample, and the resultant concentrated gas is then introduced into a detection unit (Patent Literature 1 and Patent Literature 2).
The differential-pressure method refers to a method in which the space on the permeation side is decompressed by a vacuum pump, and then a valve is once closed to isolate the space from an external environment, a test-gas-containing gas is introduced into a feed-side space, and pressure rise on the permeation side in association with gas permeation is then measured by a detection unit formed of a pressure gauge or the like (Non-Patent Literature 3). A method is also known in which a mass spectrometer is used for evaluating water vapor barrier properties of a film having high barrier properties (Patent Literature 3, Patent Literature 4, and Patent Literature 5). In the differential-pressure method, it is necessary to support the sample against the pressure difference between the feed side and the permeation side, and a technique has been disclosed in which a porous stainless steel base material (Patent Literature 3, and Patent Literature 5), a polymer/a water-permeable glass (Patent Literature 4) or the like is used.